Event Decoration does not occur with path option, despite documentation saying it will

[yaauie]

In the path-based scripting mode, common filter decoration directives (e.g., add_field, add_tag) are not run on a successful execution of the ruby filter.

e.g., with the following ruby script:

def filter(event)
 logger.info("processing event")
 [event]
end

– success.logstash-filter.rb

And the following pipeline config:

input {
  generator { count => 1 }
}
filter {
  ruby {
    path => "${PWD}/success.logstash-filter.rb"
    add_field => {"ruby" => "success"}
  }
}
output {
  stdout { codec => rubydebug }
}

– pipeline.conf

The event succeeds, but is not decorated:

╭─{ yaauie@castrovel:~/src/elastic/discuss-scratch/140375-ruby-filter-error }
╰─○ logstash-6.3.0/bin/logstash -f pipeline.conf
Sending Logstash's logs to /Users/yaauie/src/elastic/discuss-scratch/140375-ruby-filter-error/logstash-6.3.0/logs which is now configured via log4j2.properties
[2018-07-18T18:34:19,521][WARN ][logstash.config.source.multilocal] Ignoring the 'pipelines.yml' file because modules or command line options are specified
[2018-07-18T18:34:20,093][INFO ][logstash.runner          ] Starting Logstash {"logstash.version"=>"6.3.0"}
[2018-07-18T18:34:22,191][INFO ][logstash.filters.ruby.script] Test run complete {:script_path=>"/Users/yaauie/src/elastic/discuss-scratch/140375-ruby-filter-error/success.logstash-filter.rb", :results=>{:passed=>0, :failed=>0, :errored=>0}}
[2018-07-18T18:34:23,234][INFO ][logstash.pipeline        ] Starting pipeline {:pipeline_id=>"main", "pipeline.workers"=>8, "pipeline.batch.size"=>125, "pipeline.batch.delay"=>50}
[2018-07-18T18:34:23,325][INFO ][logstash.pipeline        ] Pipeline started successfully {:pipeline_id=>"main", :thread=>"#<Thread:0x739da9e8 run>"}
[2018-07-18T18:34:23,414][INFO ][logstash.agent           ] Pipelines running {:count=>1, :running_pipelines=>[:main], :non_running_pipelines=>[]}
[2018-07-18T18:34:23,527][INFO ][logstash.filters.ruby.script.context] processing event
[2018-07-18T18:34:23,898][INFO ][logstash.agent           ] Successfully started Logstash API endpoint {:port=>9600}
{
      "@version" => "1",
       "message" => "Hello world!",
    "@timestamp" => 2018-07-18T18:34:23.363Z,
          "host" => "castrovel.local",
      "sequence" => 0
}
[2018-07-18T18:34:23,948][INFO ][logstash.pipeline        ] Pipeline has terminated {:pipeline_id=>"main", :thread=>"#<Thread:0x739da9e8 run>"}
logstash-6.3.0/bin/logstash -f pipeline.conf  78.29s user 2.42s system 384% cpu 20.964 total
[success (21.000s)]